Large temperature gradients and high operating temperatures in those parts of turbine engines subjected to gases of combustion have long been known to be undesirable. High temperatures may require the use of exotic materials in constructing turbine components in order to withstand thermal fatigue and the use of such material substantially increases the cost of building a turbine. Large temperature gradients are undesirable because the large internal stresses that are generated when one part of a component operates at one temperature and another part operates at a substantially different temperature due to the difference in thermal expansion.
Consequently, it is customary to inject so called "dilution air" into the gases of combustion prior to their application to the turbine wheel and the nozzle which directs the gases thereat. Typically, it is desired to achieve a uniform circumferential mixing of the dilution air with the gases of combustion which produces a specific shape of radial temperature profile at the turbine wheel inlet which is usually not flat. However, in an optimal case, there will be complete mixing of the dilution air with the gases of combustion such that a uniform temperature of a stream of combined gases of combustion and dilution air is achieved. When such occurs, the operating temperature of the components can be adequately regulated by controlling, through suitable design parameters, the amount of dilution air in proportion to gases of combustion. At the same time, temperature gradients will be nonexistent because all parts of the gas stream being applied to the nozzle, and thus to the turbine wheel, will be at equal temperatures.
Perfect circumferential mixing cannot be obtained in practice although it may be approached in large sized turbines wherein the size of the components is such that there is substantial residence time of combustion gases and dilution air in a combustor or the like prior to application to a nozzle so as to allow fairly thorough mixing. However, in small scale turbines, the residence time is extremely short and adequate mixing will not necessarily occur without undesirably increasing the size of the components.
The present invention is directed to overcoming one or more of the above problems.